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Tracing star forming clouds at low-metallicity (astronomy)

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  • Full or part time
    Dr P Clark
  • Application Deadline
    No more applications being accepted
  • Competition Funded PhD Project (European/UK Students Only)
    Competition Funded PhD Project (European/UK Students Only)

Project Description

Practically all star formation in the Milky Way occurs in dense, massive reservoirs of gas called Giant Molecular Clouds (GMCs). Much of star formation theory thus relies on being able to constrain the total mass in molecular gas. In the Milky Way and similar galaxies, which contain gas that has a ‘solar’ metallicity (i.e. gas that has an elemental composition similar to the Sun), astronomers have to rely on the molecule CO to trace the mass of the clouds. This is because H2, which makes up the overwhelming bulk of the mass, has energy levels that are not excited at GMC temperatures (< 40K).
As we go to lower metallicities, such as those found in dwarf galaxies, the ability of CO to trace the molecular fraction in the gas breaks down, as it is easily dissociated by the light from nearby young stars. As a result, the CO emission only traces the very dense cores in low-metallicity clouds, and tells us very little about the cloud’s bulk properties. However, CO is not the only carbon-bearing species that we can observe. Both neutral, and singly ionised carbon (C and C+) are easily excited in low-metallicity clouds, and can be observed with current telescopes (ALMA/APEX/SOFIA). Preliminary results from our numerical modelling has also shown that these species are present throughout the interior of these clouds, and so may be a good tracer of cloud conditions, properties and dynamics. If this is the case, then emission from these species can provide a new probe of star-forming environments in nearby
galaxies that can help to constrain the theory of galactic evolution. In this project the student would run numerical simulations of molecular cloud formation that self-consistently combine self-gravity, (magneto)hydrodynamics, time dependent chemistry (including the main branch of carbon chemistry) and ISM thermodynamics. These simulations (similar to those in the figure) will capture the
formation of the clouds from the warm neutral medium, and follow them until they have started to produce stars. The student will then use the output from these simulations as input to a radiative transfer calculation, to obtain maps (or more exactly, position-position-velocity cubes) of the C, C+ and CO emission from the clouds. They will then be able to explore how the emission from these species traces the star formation process and properties of the host molecular cloud. The goal of the project will be to address questions such as, can we use these tracers to calculate the mass of the clouds? Do they depend on the history of cloud’s
assembly? And, are they sensitive to the star formation rate in the clouds? All these questions are of interest to the wider galactic evolution community.

Funding Notes

This project is available to students applying for funded PhD studentships and may be altered or amended.
Studentships will be awarded to successful applicants from all applications received. Applicants must satisfy RCUK residency rules for the full studentship.

Related Subjects

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